yongian best way to apply sheet masks is to do your routine including the serum/s stage, then apply the sheet mask. I leave it on for about an hour or until it dries (don't forget to use what is left in sachet on chest arms etc). Then remove, pat in the excess and continue with oil, night cream or both (I do both
) Have fun!
Attached is a photo of the very cute LRP Serozinc
minty it sounds like your skin is irritated and suffering from various problems, so I think you have to go down a simpler way. Maybe for some people it's OK to pile on lots of different stuff, but for you it's obvs not working.
Personally I also think acid 3 times a week is enough (and I have tried it more often) and since P50 is the best... Since your skin is used to acids I think you can just proceed 3 times a week but only in the PM (!), though just in case I would wet the cotton wool pad with a bit of water the first week or two to dilute it. This is strong stuff! Don't forget to use what is left of the cotton pad on chest, upper arms, elbows etc
. After that you can "graduate to the normal P50 
I also think you need to up the hydration levels and that is best done with specific products like Hylamid Sub-Q HA. At the moment I'm using TO Matryxil and am very pleased, but have a look above thread at Benton Snail Bee essence also very hydrating. You can use these serums under what you have now, like the Caudelie (I actually love and have a lot of Caudelie things). Don't know the BB though.
You can get the Caudelie Polyphenol C15 moisturiser when your is finished, I been using it for a while (with a couple of drops of oil under it). I think it's great value for money and is very hydrating.
By the way the SR GG gave me spots, not to mention the super human effort at enduring the dried cat piss smell 
As you will also see upthread - even though I have dryish skin I use the Clarins Lotus oil, which I think is the best! So maybe consider this once the natal one is finished.
Eventually you can add Vit C in the AM, but wait a few weeks until you have established a steady routine. Another step you could eventually take is adding hydrating masks a couple of times a week, but again, wait to introduce more stuff.
How many % retinol does your oil have, by the way?
Re the Clarins cleanser - when I tired it I simply felt it was not coming off properly, and the Ren cleanser is just a gut feeling that it used to be better, but I might be wrong.
Cleanse with the LRP only in the AM and for the PM just finish what you have.
So - cleanse, active (for now on in the PM), spray, hydrating serum (possibly topped wth what you still have), oil, cream (if needed) and in the AM SPF.
Yeah, this thread is a killer - but eventually you save money by first not buying stuff you have to bin and second buying some stuff that is not so expensive and is very effective (like TO or AB).
Have a think and see what you want to change and maybe ask us more specific product questions before you buy anything.